The invention relates to light emission methods and light emission devices.
Semiconductor lasers are utilized in a wide variety of applications including fiber-optic applications. The relatively small size, low input power requirements and high power conversion efficiencies of semiconductor lasers make them well-suited for fiber-optic applications.
Conventional semiconductor laser configurations are implemented as diodes typically consisting of multiple epitaxial layers provided upon an appropriate substrate, such as indium phosphide. An active layer, such as indium gallium arsenide phosphide, is sandwiched between n and p-type cladding layers of the substrate material in some conventional configurations. Opposing metal contacts are provided about the structure and a bias current is applied to the contacts to generate light at a wavelength determined by the energy gap of the active layer.
Many conventional semiconductor laser configurations are not accurately controllable to operate between a plurality of wavelengths, and it may not be desirable for the laser to vary in wavelength. In some applications, including wavelength division multiplexing (WDM) and frequency division multiplexing (FDM) applications, a plurality of lasers are precisely tuned to their respective channels for communication.
Indeed, temperature sensors and controls are utilized to maintain the operating temperature constant to avoid variances in wavelength due to temperature fluctuations.
However, in some applications it may be desirable to provide controlled emission of light at a plurality of different wavelengths. For example, such devices could be utilized in optical communication architectures which use wavelength to distinguish different information states.
The invention relates to light emission methods and light emission devices. Aspects of the invention provide methods and devices capable of emitting light at a plurality of controllable wavelengths. According to one exemplary implementation, emission of light at plural controllable wavelengths as described herein is utilized to distinguish different informational states or select a plurality of desired communication paths.
The present invention implements changes in wavelength of emitted light from a source responsive to changes in lasing mode of a laser in an exemplary configuration. In the exemplary arrangement, the lasing mode polarization of the laser is switched to implement switching of wavelength of the emitted light from the source using birefringent material in an optical path of the laser.
According to one embodiment, switching the polarization is accomplished by making the threshold for lasing of a particular polarization state less than the other. Light having the same wavelength and polarization as the desired wavelength may be selectively injected into a cavity of the source to switch the wavelength of light emitted from the source in one possible arrangement. The source typically operates in a default polarization state providing light having a corresponding wavelength.
The polarization state and the wavelength of emitted light change responsive to the injection of appropriate light. In particular, the lasing mode polarization of a laser in the cavity changes responsive to injection of external light. Birefringent material in the cavity operates to change the wavelength of emitted light from the source responsive to changes in the lasing mode polarization of the laser. Accordingly, the light is controllably injected into the cavity to control the wavelength of emitted light from the source in one exemplary embodiment.
In another implementation, electrically-controllable birefringent material is provided within an optical cavity of a source to selectively induce loss for one polarization state of a laser within the cavity enabling control of emitted light at a plurality of wavelengths. The birefringent material is controlled to control the emission of light at the plurality of desired wavelengths in such an arrangement. In one exemplary implementation, the controllable birefringent material induces loss for one polarization state responsive to control from a control signal which enables control of the operation of the laser in a plurality of polarization states. Other birefringent material within the cavity changes the wavelength of light emitted from the source responsive to changes in the lasing mode polarization of the laser.
Other implementations for controlling the polarization state of a laser are contemplated.
Accordingly, one aspect of the invention provides a light emission method. The method according to this aspect includes providing a control signal and emitting light using a laser operating in a plurality of polarization states. Adjustment of the polarization state of the laser responsive to the control signal and adjustment of the wavelength of the light responsive to the adjustment of the polarization state of the laser are provided.
The invention further discloses another light emission method. This aspect includes controlling the operation of a semiconductor laser in a plurality of polarization states. Further, emitting light having a plurality of wavelengths is provided using the semiconductor laser and corresponding to the respective polarization states.
Another aspect of the invention provides a light emission device comprising an interface adapted to receive a control signal and a laser configured to operate in a plurality of polarization states to emit light. This aspect further provides a mode selection device configured to adjust the polarization state of the laser responsive to the control signal and a wavelength adjustment device configured to adjust the wavelength of the light responsive to the adjustment of the polarization state.
As is apparent from the foregoing, the present invention has both method and structural aspects. The present invention provides methods and structures capable of accurate emission of light having a plurality of selectable wavelengths. Certain embodiments of the invention provide other advantages in addition to or in lieu of the advantages described above, as is apparent from the description below with reference to the following drawings.